The present invention relates to a field converting method for generating new field data from arbitrary field data of television signals at a special playback (variable speed playback) by a magnetic recording reproducing device, e.g., a video tape recorder (hereinbelow abbreviated to VTR), a laser disk player, etc. and device for realizing same.
When image signals recorded in a VTR, etc. are reproduced, in order to regulate playback time or to achieve special effects such as slow playback, still picture playback, fast playback, the special playback is effected, by which images are skipped (jumped) or same images are reproduced repeatedly. At this time, in order to satisfy an interlace condition of image signals or a continuity condition for subcarrier, i.e., in order to keep the continuity of field numbers, an interpolation filter technique is adopted for the purpose of preventing displacements of the center of gravity of images, i.e., the position of images, at the variable speed playback, by which image signals of a field having a different field number are generated, starting from reproduced image signals, and reducing lowering of the vertical resolution. An example of such an interpolation filter device is disclosed in JP-A-2-132984.
Further, a processing technique, in the case where the processing described above is effected by means of a digital VTR, is indicated in an article entitled "Reproduced Video Signal Processing For Composite Digital VTR", ITEJ Technical Report, Vol. 14, No. 47, pp. 13-18, Sep. 1990.
FIG. 1 indicates the interpolation filter device indicated in JP-A-2-132984.
In FIG. 1, reference numerals 401 and 402 are input and output terminals for reproduced image signals; 411 is a delay line having a delay time corresponding to a horizontal scanning period (hereinbelow called simply 1 H); 412 and 413 are delay lines having delay times of 2 H and 3 H, respectively; 421 and 428 are coefficient multipliers having a coefficient of (-.alpha./4); 422 and 427 are coefficient multipliers having a coefficient of (1/4-.alpha./4); 423 and 426 are coefficient multipliers having a coefficient of (3/4+5.alpha./4); 424 and 425 are coefficient multipliers having a coefficient of (-3.alpha./4); 431 and 432 are adders; and 441 is a switch. In this device a composite signal is separated into a luminance signal and a chrominance signal by a Y/C separating circuit and the luminance signal thus separated is inputted in the delay lines 411, 412, 413, etc. through the input terminal 401. The input signal from the input terminal 401 and the output signals of the delay lines 411, 412, 413 are inputted in the coefficient multipliers 421 and 422, 423, 424 as well as 425 and 426, 427, 428, respectively. The outputs of the coefficient multipliers 421, 422, 423 and 424 are inputted in the adder 431, while the outputs of the coefficient multipliers 425, 426, 427 and 428 are inputted in the adder 432. The outputs of the adders 431 and 432 are inputted in the switch 441. The switch 441 selects the output of the adder 432 on the H side, in the case where both the field number of the reproduced image, which is to be field-converted, and the field number of the field converted output image signal are odd or even (hereinbelow called odd or even number accordance) and the output of the adder 431 on the L side, in the case where one of them is odd and the other is even (hereinbelow called odd or even number disaccordance). Since the signal outputted by the adder 431 and the signal outputted by the adder 432 have same frequency-amplitude characteristics, there is no difference in the vertical resolution.
Therefore, even in the case where the switch is turned-over in field unit at the variable speed playback, good images can be obtained. The odd or even number accordance for the field number corresponds to a case where one of them is 1 (2) and the other is 1 or 3 (2 or 4).
Further, U.S. Pat. No. 4,641,202 corresponding to JP-A-60-545580 discloses a field converting method, by which arbitrary field data are converted into new field data, and a device for realizing same.